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72 c10 gas tank ventilation

76k5blazerr

76k5blazerr

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Alright so I've only had this c10 for a few weeks. When I got it I didn't seem to notice this issue. Maybe it just started happening, which is so as far as I can tell. Anyway yesterday I first noticed a gas smell while driving it, then got where I was going and got out of the truck and loosened the gas cap, WHOOSHHHH, out comes lots of vapor/pressure from the gas tank. Then I put it back on, looser to help with venting and drove some more, noticed the gas smell after a few minutes, loosened the cap, same thing, WHOOSHHHH. So I thought maybe my gas cap vent wasn't working because the cap is old and rusty so I went to autozone just now and bought a new cap, put it on and drove home, smelled fumes on the way home, loosen cap, whoooosh, same thing, lots of vapor pressure came out. So now I'm thinking that the fuel vent line from the tank may be clogged or something. What do you guys think and what should I start checking.
 
You might have a pinched vent line . Does it have emisions equipment like a charcoal canister ? Might have something to do with it. I can remember a couple cars wooshing like that when you take the fuel cap off, but not an old c-10. I don't think it is anything to worry about ,though.
 
The 2 that I have had, ('72s) there was a line coming off of the passenger side of the tank that hooks to a loop up inside the cab beside the rear window. It's between the inner and outer walls. This is connected to a line that went to the charcoal canister up in the inside if the front fender. (Right side, IIRC) then that was connected to the carb. I think, but I can't remember for sure, that the earlier trucks had a vented cap and the '72 wasn't. I don't remember for sure..
The problem with the vented cap is that it is one more way for gas to spill down the side of the cab when it doesn't hold. The gasket on the cap has a hard time sealing against a full tank sloshing anyway. So if your cap is holding that well, look at the vent lines. The loop up in the cab makes sense to me, but it may not do as much as I think. ..?
 
I've always heard the in cab tanks will stink no matter what you do, no personal experience with them here as I have a blazer. K85 Octane went the route of putting one uner the bed on his swb c10. If its still hooked up original the vent tube would make its way up to the charcoal canister, which if like the blazer would be over by the pass side battery(i believe). It is most likely either a vent line or canister that is plugged up. Many (most) guys on here will say to ditch the canister and just run a vent in a way that wont stink up your cab. Only down side of this is you can get fuel smell when left in an enclosed space like a garage.

Edit:6872's explanation is great
 
Boy, I am trying really hard to remember a carbon canister or even a vent tube on my '68. Like 6872xtc said, maybe the older trucks didn't have one. I drove my truck for about 2 weeks and never noticed any smell. But that sounds like your story as well.

Spit balling here.....
Make sure the cap you bought it vented.
Try driving the truck next time without the cap on (obviously without a full tank) and see if you get the smell.
Maybe even unbolt the tank and tilt if forward to check for leaks on the back side. Never know
Maybe a PO pulled the canister out. It's not hard to put one back in and works better than an open air vent.

I can't see all these "new" truck owners, back from the 50s with tanks inside, all complaining about gas smell. They must have had it under control :dunno:
 
I was looking for older caps for the '73-ish trucks since some used vented caps, I never did find one that was vented, even though stant and the like sold the non-vented caps for applications that required venting.

The vented caps vent at almost zero pressure. Take it off the tank and see if you can easily blow through it. If you can't, it's not vented, or not working right. I would not be surprised if new manufacture is non-vented even when it should be.
 
dyeager535 said:
I was looking for older caps for the '73-ish trucks since some used vented caps, I never did find one that was vented, even though stant and the like sold the non-vented caps for applications that required venting.

The vented caps vent at almost zero pressure. Take it off the tank and see if you can easily blow through it. If you can't, it's not vented, or not working right. I would not be surprised if new manufacture is non-vented even when it should be.
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The cap I bought is supposed to be vented. I'll check it today. My buddy said the same thing happened to his 69 bronco and he had to drill a hole in the cap. I've got a lot of work to do on the truck this weekend so will check the vent lines then. I don't think I still have the charcoal can there.
 
dyeager535 said:
I was looking for older caps for the '73-ish trucks since some used vented caps, I never did find one that was vented, even though stant and the like sold the non-vented caps for applications that required venting.

The vented caps vent at almost zero pressure. Take it off the tank and see if you can easily blow through it. If you can't, it's not vented, or not working right. I would not be surprised if new manufacture is non-vented even when it should be.
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Took the cap off and blew in it, couldn't get any air through. It has a vent though, think it's just not working? Should I go back to autozobe and exchange it? Or would there be any cons to drilling a small small hole right through the center of the cap?
 
I suppose you could drill a hole, but if it's got the standard rubber valve that you can see the stem of, with a small metal pick/screwdriver you can probably move the rubber enough to inactivate the valve so it just acts as a breather hole. It's what I ended up doing. At least the later caps are pretty easy to completely disassemble, not sure about what you have, but might be worth looking at. If you kept your old one, you have one to play with. :)

It's really not a good idea to have an un-vented cap, as dust/junk WILL work it's way into the tank, but it's not going to be the end of the world, especially when given little in the way of options.

I don't like non-vented caps because on the K5 with a full tank, climbing mountain roads it will dump plenty of fuel out of the cap, but I'm guessing a non-issue with your application.

You could go back to the store, but if it was "bad" out of the box, I expect it's probably just the wrong thing being sold for your application and I'd not expect any different out of the next one.
 
dyeager535 said:
I suppose you could drill a hole, but if it's got the standard rubber valve that you can see the stem of, with a small metal pick/screwdriver you can probably move the rubber enough to inactivate the valve so it just acts as a breather hole. It's what I ended up doing. At least the later caps are pretty easy to completely disassemble, not sure about what you have, but might be worth looking at. If you kept your old one, you have one to play with. :)

It's really not a good idea to have an un-vented cap, as dust/junk WILL work it's way into the tank, but it's not going to be the end of the world, especially when given little in the way of options.

I don't like non-vented caps because on the K5 with a full tank, climbing mountain roads it will dump plenty of fuel out of the cap, but I'm guessing a non-issue with your application.

You could go back to the store, but if it was "bad" out of the box, I expect it's probably just the wrong thing being sold for your application and I'd not expect any different out of the next one.
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I'll post a pic of my cap later. I've been reading about a mod you can do to the spring inside the cap to make it vent at .5 PSI instead of like 6 psi. From what I've read my cap is vented but the vent doesn't open until 6 pounds of pressure. You can cut the spring down to make it vent earlier. Assuming they were talking about the same style cap I have.
 
I tried to find pics of the "older" style gas cap valve assembly I'm familiar with, but all I can find are pics of late-model assemblies. The ones I'm familiar with it's pretty easy to pop the entire inner-piece off of the cap, then disassemble from there.

I don't know what human "lung pressure" is, but I know when I got my older gas cap (pre-stant lol) I could easily blow through it. On the later ~16PSI caps, not possible for me to blow through them.

No idea what pre-emissions caps are *supposed* to vent at.
 
C
dyeager535 said:
I tried to find pics of the "older" style gas cap valve assembly I'm familiar with, but all I can find are pics of late-model assemblies. The ones I'm familiar with it's pretty easy to pop the entire inner-piece off of the cap, then disassemble from there.

I don't know what human "lung pressure" is, but I know when I got my older gas cap (pre-stant lol) I could easily blow through it. On the later ~16PSI caps, not possible for me to blow through them.

No idea what pre-emissions caps are *supposed* to vent at.
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Cut the spring down inside the cap. Now I can blow through it with ease. Should be good now
 
Idiotic they can't even make gas caps correctly. My suspicion is that they don't want to deal with the repercussions of people being able to get vented caps for non-vented applications, so they screw people like yourself.

Only a suspicion, but since they are interchangeable, other than utter incompetency, only excuse I can come up with for them.

Glad you got it working properly. Or at least I *hope* it's now working right. :)
 
dyeager535 said:
Idiotic they can't even make gas caps correctly. My suspicion is that they don't want to deal with the repercussions of people being able to get vented caps for non-vented applications, so they screw people like yourself.

Only a suspicion, but since they are interchangeable, other than utter incompetency, only excuse I can come up with for them.

Glad you got it working properly. Or at least I *hope* it's now working right. :)
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Drove it awhile today, took the cap off when I got home, no whooooshh. Success. :burnout:
 
oooooo custom/10 double trim and stainless window trim

needs sport bumper though :D

how close to original is this thing? Looks super clean


X001-Y002.jpg
 
K85 Octane said:
oooooo custom/10 double trim and stainless window trim

needs sport bumper though :D

how close to original is this thing? Looks super clean


X001-Y002.jpg
Click to expand...
It's pretty original, has original 350, rebuilt with 2k on it. The paint color is the original dark olive. It still has the glovebox option sticker. Sheetmetal seems to be solid with no rust that I've found though the body isn't perfectly perfect. I'm really starting to enjoy it. It gets lots of waves and thumbs ups.
 
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